This invention relates to apparatus for illuminating an object and for providing a uniform, thin line of light onto an object for line scan applications. More specifically, the invention relates to light line units of modular design that can be butted end to end to provide very long, seamless linear beams of light. The invention is more particularly directed to an optical fiber based unit which can conduct light from a remote light source and convert the illumination from that source into a thin, long line of light.
Light line units are employed in a variety of applications where a long, narrow strip of light is needed. Light line units can be used in line scan applications, e.g., with line-scan type CCD cameras in web-type applications. The current preference for a light line unit employs a fluorescent tube and an elongated aperture to produce a line of light. The fluorescent tube light line units have difficulty producing a line of light that is uniform from one end of the line to the other, or a light that remains uniform over time. The fluorescent units have temperature-sensitive output fluctuations, and outputs that vary with age and with other conditions. Also, if two units are to be joined to provide a light line of extra length, there is additional illumination drop-off between modules.
Optical fibers have been used as line illuminators, and one example is described in U.S. Pat. No. 4,952,022 to Genovese. In the Genovese patent, the illuminating device is comprised of a bundle of large-diameter fibers, in which the distal ends or termini are deformed into a rectangular cross section. There, the idea was to produce a linear beam that is uniform along the output of the array. However, the patent does not address how to join two or more units to produce a very long linear beam with no drop-off or discontinuity from one modular unit to another. Another system for transmitting a linear beam of light from a lamp to a workpiece using optical fibers is described in U.S. Pat. No. 3,192,843 to Kapany et al. In the system of that patent, there are alternating layers of illuminating fibers and imaging fibers, and no provision for joining a number of traits end-to-end for any reason.
In a number of industrial applications, it is necessary to provide a line of illumination up to several meters in length, and with uniformities of better than 10% in a transmission or reflective mode. A typical application can be automated quality inspection of a web type product that travels past, for example a fabric or carpet. The quality of the inspection depends entirely on the uniformity of the light source, that is, on uniformity across the light line. Such high uniformity has been difficult to achieve using standard techniques, such as apertured fluorescent lamps. In addition, inspection of heat-sensitive materials requires remoting the light source from the product, and this has been impossible with conventional linear light sources.